Is Sienna heading for the boardroom or beach?

No one was sure whether it was a business suit or a bathing suit. But if its function was to turn heads, it was a success.

Sienna Miller appeared to be confusing the Big Apple with the beach as she strolled through New York in a halterneck swimsuit/miniskirt combination.

From the front, with the help of a stylish trilby, she looked as though she might be heading for Wall Street.

But from the back, it could only have been the sands of Long Island she had in mind.

The look is a stark contrast with the hippie chic with which she inspired women to fill their wardrobes with flowing skirts and kaftan tops last year.

Whether it will gather the same copycat devotion remains to be seen. Miss Miller, 23, was in the city’s Little Italy district for lunch with boyfriend Jude Law, who cut a relatively shabby figure in baggy shirt, loose shorts and a straggly beard.

Her revealing back view suggested she may have regained some of the weight she lost for her last film role. Earlier this year she told how she had lost half a stone to play Andy Warhol’s waif-like muse Edie Sedgwick in Factory Girl.

An onlooker said: ‘She looked stunning in her swimsuit ensemble. It was very revealing and ensured she was the focus of attention.’

The New York trip comes just days after the actress was spotted taking a break in Antibes, in the South of France, with her sister.